Dust polarized emission observations of NGC 6334

BISTRO reveals the details of the complex but organized magnetic field structure of the high-mass star-forming hub-filament network^★

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: Doris.Arzoumanian@astro.up.pt
² Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
³ Institute of Liberal Arts and Sciences Tokushima University, Minami Jousanajima-machi 1-1, Tokushima 770-8502, Japan
⁴ National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Dominion Radio Astrophysical Observatory, Herzberg Astronomy and Astrophysics Research Centre, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada
⁶ Department for Physics, Engineering Physics and Astrophysics, Queen’s University, Kingston, ON, K7L 3N6, Canada
⁷ National Astronomical Observatory of Japan, NAOJ Chile, Alonso de Córdova 3788, Office 61B, 7630422 Vitacura, Santiago, Chile
⁸ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁹ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁰ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada
¹¹ Academia Sinica Institute of Astronomy and Astrophysics, No.1, Sec. 4., Roosevelt Road, Taipei 10617, Taiwan
¹² Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹³ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
¹⁴ University of Science and Technology, Korea, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
¹⁵ Department of Physics, Faculty of Science and Engineering, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan
¹⁶ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁷ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK
¹⁸ Laboratoire d’Astrophysique (AIM), CEA/DRF, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
¹⁹ Centre de recherche en astrophysique du Québec & département de physique, Université de Montréal, 1375, Avenue Thérèse-Lavoie-Roux, Montréal, QC, H2V 0B3, Canada
²⁰ East Asian Observatory, 660 N. A’ohōkū Place, University Park, Hilo, HI 96720, USA
²¹ Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
²² CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences, PR China
²³ National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012, PR China
²⁴ Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan
²⁵ Department of Physics and Astronomy, University College London, WC1E 6BT London, UK
²⁶ Department of Earth Science Education, (SNU), 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
²⁷ Department of Astronomy, Yunnan University, Kunming, 650091, PR China
²⁸ Departamento de Astronomía, Universidad de Concepción, Av. Esteban Iturra s/n, Distrito Universitario, 160-C, Chile
²⁹ Centre for Astronomy, School of Physics, National University of Ireland Galway, University Road, Galway, Ireland
³⁰ SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, Moffett Field, California 94035, USA
³¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
³² Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
³³ School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, PR China
³⁴ Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education, Nanjing 210023, PR China
³⁵ SKA Organisation, Jodrell Bank, Lower Withington, Macclesfield, SK11 9FT, UK
³⁶ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK
³⁷ Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing, PR China
³⁸ Institute of Astronomy, National Central University, Zhongli 32001, Taiwan
³⁹ Department of Astronomy and Space Science, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea
⁴⁰ School of Physics, Astronomy & Mathematics, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
⁴¹ Vietnam National Space Center, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
⁴² Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK
⁴³ Department of Physics and Astronomy, The University of Manitoba, Winnipeg, Manitoba R3T2N2, Canada
⁴⁴ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
⁴⁵ Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
⁴⁶ Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴⁷ Subaru Telescope, National Astronomical Observatory of Japan, 650 N. A’ohōkū Place, Hilo, HI 96720, USA
⁴⁸ Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond Street, London N6A 3K7, Canada
⁴⁹ Hiroshima Astrophysical Science Center, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁵⁰ Department of Physics, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁵¹ Core Research for Energetic Universe (CORE-U), Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁵² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁵³ Astronomical Institute, Graduate School of Science, Tohoku University, Aoba-ku, Sendai, Miyagi 980-8578, Japan
⁵⁴ Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 Canada
⁵⁵ Department of Physics and Atmospheric Science, Dalhousie University, Halifax B3H 4R2, Canada
⁵⁶ Department of Space, Earth & Environment, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
⁵⁷ School of Space Research, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea
⁵⁸ CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences, People’s Republic of China; University of Chinese Academy of Sciences, Beijing 100049, PR China
⁵⁹ School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, PR China
⁶⁰ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing 210023, PR China
⁶¹ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
⁶² Faculty of Education & Center for Educational Development and Support, Kagawa University, Saiwai-cho 1-1, Takamatsu, Kagawa, 760-8522, Japan
⁶³ Department of Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁶⁴ SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan
⁶⁵ Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
⁶⁶ Astrophysics Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK
⁶⁷ Kavli Institute for Cosmology, Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁶⁸ Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
⁶⁹ Department of Physics, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
⁷⁰ Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁷¹ University of Science and Technology of Hanoi, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
⁷² Jet Propulsion Laboratory, M/S 169-506, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁷³ University of South Wales, Pontypridd, CF37 1DL, UK
⁷⁴ Department of Applied Mathematics, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
⁷⁵ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁷⁶ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷⁷ School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK

Received: 9 June 2020
Accepted: 18 December 2020

Abstract

Context. Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained.

Aims. We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation.

Methods. We present new observations of the dust polarized emission at 850 μm toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with the James Clerk Maxwell Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (PI), the polarization fraction (PF), and the plane-of-the-sky B-field angle (χ_{B_POS}) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and χ_BPOS along the ridge crest and compared them with the results obtained from simulated filaments.

Results. The observations span ~3 orders of magnitude in Stokes I and PI and ~2 orders of magnitude in PF (from ~0.2 to ~ 20%). A large scatter in PI and PF is observed for a given value of I. Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc), χ_BPOS varies coherently along the crests of the filament network. The observed power spectrum of χ_BPOS can be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that of I. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, χ_BPOS rotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in PF toward the high-column density (N_H2 ≳ 10²³ cm⁻²) star cluster-forming hubs. These latter large PF values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure.

Conclusions. These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.